1. Field of the Invention
The present invention relates generally to a printing apparatus, and more particularly to an arrangement for adjusting or changing the printing condition of a print head of the printer.
2. Discussion of the Prior Art
A printing apparatus commonly has a platen for supporting a recording medium, and a print head for effecting a printing operation on the recording medium. The printing operation takes place while the print head is moved along the length of the platen. The apparatus generally accepts different types of recording medium which have different thicknesses, and even accepts two or more sheets of paper or other recording media which are superposed on each other. Thus, the thickness of the recording medium or total thickness of the media is not constant. For assuring excellent printing quality, it is required to adjust the printing condition of the print head, depending upon the specific thickness of the recording medium or media. The term "printing condition" used herein is interpreted to mean a condition that influences the printing quality, such as a so-called head gap which is a distance between the print head and the surface of the platen, or a printing pressure which is applied to the recording medium from a suitable printing element or elements such as dot matrix print wires. An appropriate device or devices are required to change or adjust a selected parameter or parameters (e.g., head gap or position of the print head with respect to the platen, or printing pressure) of the printing condition.
An example of such a device for adjusting the printing condition on a printer is disclosed in laid-open Publication No. 62-193866 of unexamined Japanese Patent Application, wherein the thickness of a recording paper is detected by a paper thickness sensor, to adjust the head gap depending upon the detected paper thickness. The printer disclosed in this publication is operated in two modes associated with the adjustment of the head gap. The modes are selected by a selector switch when printing is effected on cut sheets. In the first mode, the thickness of each cut sheet is detected when the printer is loaded with the cut sheet. The second mode is selected when printing is effected continuously on successively supplied cut sheets having the same thickness. In this second mode, only the thickness of the first or initially supplied cut sheet is detected by the sensor, and the head gap is adjusted based on the detected thickness of the first sheet. The adjusted head gap is kept unchanged for the following sheets, whereby the printing operation can be performed in a relatively efficient way.
In the printer disclosed in the above-identified publication, it is necessary to provide suitable means for determining the first or initially supplied cut sheet, in order to command the paper thickness sensor to detect the thickness of the supplied sheet. However, the publication does not described such mean.